Refining an established model of hypertension in the mouse

Aims

This project aims to refine a well-established mouse model of hypertension.

Background

Hypertension occurs in about 30% of the population, 50% of elderly people, and leads to cardiovascular diseases such as stroke and heart. Mice models are commonly used in research on hypertension and the investigation of potential treatments. Over 1,000 mice undergo the surgical procedures associated with hypertension modelling each year in the UK; with many more used for related blood pressure studies associated with phenotyping, drug testing, obesity, and ageing studies. Any refinement of these techniques has the potential to minimise the stress caused to these animals.

The current ‘gold standard’ method for studying blood pressure in mice involves two invasive surgeries; the first to implant a radio-telemetry probe to allow measurements from freely-moving conscious mouse in their home cage and the second to introduce a 1cm long osmotic mini-pump releasing angiotensin-II (Ang II) which increases blood pressure.

Research details and methods

The research will investigate two possible refinements to the Ang 11-induced hypertension mouse model. The first is whether a commercially available pellet can be used instead of the bulky mini-pump to deliver a similar profile of hypertension and vascular remodelling. The second is whether a non-invasive tail cuff can be used to measure blood pressure. This approach is used, but there are concerns about the impact of handling on the animals’ blood pressure. New research on refined methods of handling mice provides an opportunity to re-visit this as an alternative to radio-telemetry.

The primary objective of this studentship is to refine a commonly used murine model of hypertension. The "gold standard" technique for blood pressure measurement involves surgically-implanted radio-telemetry probes to allow measurements on the freely-moving conscious mouse in its home cage. This is routinely twinned with angiotensin-II (Ang II)-induced hypertension. However, Ang II is administered via a bulky osmotic mini-pump, implanted via a second surgical episode (10-14 days after the first surgery). The use of an alternative non-surgical tail-cuff plesmythography technique to measure blood pressure, has lost favour as it involves restraint and gives higher readings due to stress. Thus the measurement techniques to assess chronic Ang II-induced hypertension in the mouse involve either two major surgeries or one surgery and restraint stress. We hypothesise that we can refine this study in terms of i) replacing the bulky osmotic mini-pump with a substantially smaller pellet and ii) refining the tail-cuff technique through improved handling techniques and pre-exposure to the restraint tube. Firstly, we will examine whether an Ang II-containing commercially prepared pellet produces a similar profile of hypertension and vascular remodelling, when compared with that of the Ang II mini-pump. This will be examined through use of radio-telemetry to measure blood pressure. The mice tissues will be subjected to a range of analyses ex vivo, to ensure that the biomarkers of hypertension are maintained with the refined technique. The successful use of the pellet will provide impact in terms of a major refinement on the welfare over the lifetime of the mouse, whilst continuing to allow a detailed analysis of the molecular/biochemical influence of hypertension on the mouse pathology. The second aim of this project is to investigate handling methods associated with the use of the tail-cuff technique and to determine the influence on blood pressure. We will utilise recent NC3Rs research to examine the impact of handling on the mice. We will measure hypertension after the typical technique of holding by the tail and forcing mice into the restraining tube. We will compare this with handling via a tube and transferring the mouse from the tube to the restraint cone, in a seamless manner. Finally, and possibly most importantly, we will determine the importance of placing the restraint tube in the mouse's home cage so that it becomes familiar with it, before use. In each case, blood pressure will be compared, as measured by the tail-cuff, in the home restraint tube. The measurement of blood pressure will allow us to directly determine the impact of the improved handling and acclimatisation to the tube to each individual. The ultimate output from this research is one where we are able to achieve a situation where we can robustly defend and demonstrate the use of injectable pellets and tail-cuff, thus reducing surgery to a simple procedure and the implant to a single small pellet and stress to a level where blood pressure is not influenced. However, the separate end points of refining the model so that we demonstrate similar hypertension and pathology associated with the injectable pellet are also major steps forward. It will be important to publish the results in major journals (e.g. Nature Protocols). Also, to present at meetings, in order to reach the wider hypertension community. A major aim here is to target the very referees who demand that telemetry be used, without worry about the surgical consequences as they just assume that the stress associated with the tail-cuff measurements is going to invalidate results. We consider >1,000 mice experience this specific technique per year, with many more used for related blood pressure studies associated with use for phenotyping, drug testing, obesity and ageing. The student will receive a cutting edge cardiovascular training and communication skills all with a key focus on refinement.